A typical form of fluid flow machine wheel comprises an inner hub portion and an outer hub portion which are connected together to form a hub to be mounted on a shaft, with blades or vanes projecting away from the outer hub portion. It has been found that when a fluid flow machine wheel of that kind is used in relation to a medium involving uncontrolled hydraulic conditions or properties such as waste water, sewage, feces, liquids carrying sludge or slurry, or the like, it is virtually inevitable that the wheel suffers from shocks, impacts and knocks as a result of changing operating conditions such as varying consistency of the medium passing through the machine. Such effects on the wheel can result in undesirable vibration phenomena and in an extreme case can even result in irreversible damage to the wheel or a drive motor connected thereto, a transmission assembly, mountings for same, and so forth.
A bladed wheel for a suction cleaner is to be found in German patent specification No. 578 128, comprising a shaft hub involving an inner hub portion and an outer hub portion, with blades projecting away from the outer hub portion. Disposed between the inner hub portion and the outer hub portion is a hub damping element of an elastic material which is intended to provide a sound-damping action. Shocks or impacts as are possible or inevitable in the case of a fluid flow machine wheel of the kind to which the invention relates, in use in the above-indicated circumstances involving a medium entailing uncontrolled hydraulic conditions or properties are not relevant in regard to such suction cleaner impellers.
German patent specification No. 759 535 describes a fan impeller of which the blades are connected to a motor shaft with the interposition of disks or the like of elastic rubber. The blades are secured to the rubber disks individually and separately from each other in such a way that the masses thereof are connected together only by way of the rubber disks but do not have any contact with each other. That impeller therefore does in fact have an inner hub portion, but there is no outer hub portion. On the contrary, in that arrangement the blades are independent components which are separate from each other.
Shocks and impacts as in the case of a fluid flow machine wheel involving the circumstances with which the present invention is concerned are also not to be expected with the impeller of German patent specification No. 759 535.